The present invention relates to a dynamic testing system that applies force loads to a test specimen. More particularly, the present invention relates to a tensile testing system that applies tensile loads to a test specimen for the measurement of mechanical properties thereof.
Material testing systems that apply force loads to test specimens are known. Generally, such a system includes opposed holders that grip a specimen therebetween. An upper holder is joined to a crossbeam that moves relative to a lower holder. A load cell joined to the upper holder provides a signal indicative of tension or compression forces applied to the test specimen.
These material testing systems typically use a screw drive or hydraulic extension mechanism. The load cell for determining force used in these systems is chosen either for high sensitivity or for high load. Load cells with high rigidity however result in a lower sensitivity to displacement. Conversely, sensitive load cells can apply a lower maximum force to the test specimen.
Traditional testing machines however can not accommodate some test specimens of which mechanical properties are desired. In particular, the unique geometry of the test specimens and the dynamic mechanical properties desired makes the use of traditional material testing systems difficult, if not impossible. For example, determining mechanical properties of fibers with diameters of 1 to 60 microns is difficult with traditional testing systems. In addition, advances in polymer technology present the need for evaluation of tensile loaded materials beyond traditional yield, modulus and failure properties.
Accordingly, there is a need for a test system that can be used for small diameter test specimens. Results obtained therefrom can then be used to measure dynamic properties of these unique test specimens.
The present invention provides a material testing system having a base and first and second test specimen holders. A first displacement sensor measures displacement of the first specimen holder relative to the base. A second displacement sensor measures displacement of the second specimen holder relative to the base.
Another aspect of the present invention includes a material testing system having first and second specimen holders. A first actuator is coupled to the first specimen holder and a second actuator is coupled to the second specimen holder. A controller is coupled to the first and second actuators. The controller operates the first actuator to cause displacement of the first specimen holder and further operates the second actuator to dispose the second specimen holder in a known position.
In addition, a method is provided for determining elastic and plastic properties of materials. The method includes attaching a specimen to a first holder and a second holder and displacing the first holder away from the second holder. The method further includes applying a force to the second holder in a direction opposite displacement of the first holder and simultaneously measuring extension of the specimen with a first sensor and measuring force on the specimen with a second sensor.